The present invention is related to a device for driving a double seat valve with two closing elements, arranged in series and movable with respect to each other, which in the closed position of the double seat valve prevent the overflow of fluids from one valve housing part into another one through a connection opening connecting these valve housing parts of a valve housing with each other, and which in the closed position as well as in the open position of the double seat valve limit a leakage cavity that is connected to the surroundings of the double seat valve. In this, the second closing element is realised greater in diameter than the first closing element, so that the double seat valve opens in the direction of the second closing element as a consequence of this, an opening towards the downside being preferred. The device is destined to generate the opening and closing movements of the closing elements (fully open position H), and furthermore to transfer the closing elements into their respective seat cleaning position (partially open positions T1, T2), in order to rinse and clean the coaxial seating areas associated to the closing elements. The displacement rods of the closing element interlace telescopically into each other, and at one side, they are guided out of the valve housing and into the device.
For generating the opening and closing movement (fully open position H) of a double seat valve discussed here serves a so-called main displacement mechanism, and so-called individual displacement mechanisms are provided for generating each of the partially open positions T1 and T2. When the main displacement mechanism and the individual displacement mechanisms are housed in one common housing, one speaks of a so-called “integrated” drive device. A drive device for double seat valves referring to this is described in EP 0 868 619 B1 or in WO 2005/093299 A1, for instance.
From DE 31 33 273 C2, a drive device for double seat valves is known in which the individual displacement mechanisms for the respective partially open position are each additively inserted as autonomous displacement devices between the main displacement mechanism and a lantern housing. The main displacement mechanism generates exclusively the full stroke for the fully open position. The addition of the individual displacement mechanisms requires no change of the adjacent standard components of the main displacement mechanism and the lantern housing. The advantages achievable with this so-called “modular” drive concept are in particular that a much standardised double seat valve having a standard drive for the generation of the fully open position receives special functions by additive insertion of relatively simple individual displacement mechanisms, like the generation of partially open positions of the two closing elements.
In principle, one distinguishes between double seat valves that open towards the downside (for instance EP 0 646 741 A1) or towards the upside (for instance DE 196 08 792 C2).
A so-called leakage-free switching double valve arrangement which has essential features of the double seat valve capable of seat cleaning mentioned in the beginning is known from EP 0 646 741 A1. This double seat valve has two closing elements embodied as slide pistons, it opens towards the downside with respect to vertical standard position, and the drain of the leakage cavity takes place towards the downside also, namely via a pipe-shaped shaft that is formed on the downside situated closing element and in which a drain bore is disposed and which is guided towards the downside out of the valve housing. Independently from each other, by a partial stroke directed opposite to the opening movement, each of the two closing elements can be transferred into a rinsing position in which the respective closing element is free from its valve seat and rests on a housing stop that is provided with passages for a rinsing agent. In this, the passages for rinsing agent limit the amount of cleaning agent in the respective seat cleaning. The closing elements are actuated via displacement rods, which are both guided towards the upside, out of a valve housing and into a drive. In order to permit disassembly of the smaller upper closing element and of the lower greater closing element in one action towards the upside, the valve seats are provided with sealing rings that are held by housing inserts. These housing inserts are inserted into the valve housing from out the side facing the pipe-shaped shaft.
In the double seat valve of EP 0 646 741 A1, it is advantageous, like in all other double seat valves which open towards the downside and have a leakage drain guided out of the valve housing towards the downside, that in the open position of the double seat valve, the passage cross section of a connection opening connecting the two valve housing parts with each other is not narrowed by the cross section of the leakage drain. This reduces the rated width of the valve housing, determined by the passage cross section of the connection opening, for one to two standard widths in particular then when the passage cross section of the leakage drain between leakage cavity and surroundings of the double seat valve has to be equal to the greatest passage cross section of the pipeline connected to the double seat valve, as required in the USA for instance.
In the double seat valve of EP 0 646 741 A1, it is disadvantageous that this switches at best in a leakage reduced, but not as the title pretends leakage free manner. The switching leakage results from the fact that in the space that is limited between the two seat seals at the valve housing side on the one hand and at the closing element side on the other hand, liquid is included upon every opening or closing stroke, and that this liquid arrives in the leakage cavity and from there in the leakage drain after the separation of the two closing elements on the central seal that acts between the two. It is further disadvantageous that the respective seat cleaning flow, which arrives through the rinsing agent passages on the associated housing stop and is predominantly axially/radially oriented, impinges in a more or less uncontrolled and turbulent manner on the seat seal of the other closing element that is in the closed position.
With the double seat valve of EP 0 646 741 A1, the amount of cleaning agent can be limited in the respective seat cleaning as desired. However, the requirements which are imposed to such a double seat valve in certain countries are even more extensive. For instance, in the USA it is required that upon greater seal failures or even upon the loss of one of the two seat seals during the seat cleaning of the other closing element, no cleaning agent may pass through via the respective seal failure or the seat region without seat seal. Under these circumstances, such a double seat valve is imposed the requirement not only to limit the amount of cleaning agent and to avoid a direct impingement thereof on the seat regions during the seat cleaning, but also to discharge the seat cleaning flow with as little turbulences as possible into the leakage cavity at first and from there into the surroundings, without that the respective closed seat region is directly flown against or impinged under pressure increase by this seat cleaning flow.
With direct impingement is meant every velocity component of the respective seat cleaning flow that is directed vertically against the walls that limit the seat region. Namely, it has proven that each direct impingement related to this results in a conversion of kinetic flow energy into static pressure. Depending on the impact angle of the flow on the wall- or body surface that is flown against, a branch flow with a so-called branch streamline results, the latter dividing the flow into two halves. The branch streamline itself impinges onto the so-called stagnation point, so that the velocity is zero at this point. The pressure increase occurring as a consequence of this stopping down of the velocity is also designated as ram pressure. The pressure increasing mechanisms pointed out above generate a leakage flow via the respective choke gap and the deficient or no more present at all seat seal. Thus, any direct impact of the seat cleaning flow on the surfaces limiting the leakage cavity is counter-productive in every case.
A double seat valve that opens towards the upside with respect to a vertical standard position and is capable of seat cleaning is known from DE 196 08 792 C2. In this double seat valve, the amount of cleaning agent in the respective seat cleaning can be controlled by so-called choke gaps and can be assessed very narrowly. Furthermore, a direct impact on the respective closed seating area during the seat cleaning of the other seating area is prevented by guiding and directing the seat cleaning flow.
The double seat valve of DE 196 08 792 C2 is provided with two so-called seat cleaning positions, wherein the first seat cleaning position is generated by a first partial stroke directed opposite to the opening stroke. In this position, the cylindrical lug disposed on the first closing element at the leakage space side forms a so-called choke gap with the associated cylindrical first seating area, via which the amount of cleaning agent supplied from the neighbouring first valve housing part can be limited. The seat cleaning position of the second closing element takes place by a second partial stroke directed like the opening stroke, wherein in the partially open position, the cylindrical lug disposed on the second closing element at the leakage space side forms a second choke gap with the associated part of the connection opening, which limits the amount of the second seat cleaning flow generated in this seat cleaning position.
Because the two closing elements and the associated cylindrical lugs have different diameters, the respective associated portions of the connection opening have also different diameters, so that a transition area results between these two diameters. In the seat cleaning position of the first closing element, the first seat cleaning flow flows along the cylindrical seating area and hits the front side limitation on the second closing element, wherein at least a direct impact of the first seat cleaning flow on the second choke gap, and by this on the seat region of the second closing element, is prevented through the diameter difference of the two portions of the connection opening. In the seat cleaning position of the second closing element, the second seat cleaning flow is radially deflected towards the inside on the transition area that bridges the diameter difference between the portions of the connection opening, and is guided past the upper front side periphery of the first closing element. Even in this case, a direct impact of the second seat cleaning flow on the first choke gap and by this on the seat region of the first closing element is prevented through this.
From WO 2007/054131 A1, a double seat valve that opens towards the upside and is capable of seat cleaning is known, which is improved against the previously described state of the art amongst others in that a discharge of the seat cleaning flow, as free of turbulences as possible, into and out of the leakage cavity is secured and a pressure-increasing direct impact on the seat regions is safely avoided. This is achieved amongst others by a transition area between the two seating areas of the closing elements and an annular recess in the form of a special deflection area in the dependently driven greater closing element. A central seal is arranged between the two closing elements, so that even in this closing element configuration, one might rather call it a leakage-reduced than a leakage-free switching in the strict sense.
From WO 2007/054134 A1, a double seat valve that opens also towards the upside and is capable of seat cleaning is furthermore known, which is improved against the previously described state of the art according to WO 2007/054131 A1 in that it switches without leakage to a very large extent. This is achieved in that at its end facing the smaller, independently driven closing element, the dependently driven greater closing element has a recess with an essentially cylindrical circumference wall falling in line with the seating area of the smaller closing element, and the recess is dimensioned such as to sealingly receive an end portion and a radial seal of the smaller closing element during the opening movement before the greater closing element opens.
DE 196 18 235 C1 describes a double set valve opening towards the downside with a controlled leakage space, which is equipped with two sealing sites which are arranged in series and in planes that are parallel to each other and which prevent the overflow of fluids from one valve housing part into the other in the closed position of the double seat valve. The leakage space is arranged between the sealing sites and connected at the valve housing side with the surroundings of the double seat valve. The double seat valve has three translationally displaceable closing parts, each realised like a slide. A first closing part is displaceable between a closed and an open position, wherein in the opened position of the double seat valve, it connects the inner spaces of the two valve housing parts with each other via a passage opening that is provided therein radially at the inside. In the closed position of the double seat valve, the above mentioned first closing part realises the first sealing site with the first valve housing part on the one hand. On the other hand, in the closed position of the double seat valve, a second closing part forms the second sealing site with the second valve housing part. In every other position than in the opened position of the double seat valve, a third closing part is sealingly displaced within the passage opening, and during the opening movement of the double seat valve, it sealingly rests on the second closing part and is transferred into the open position with the same.
Each of the three closing parts has one displacement rod, which is guided into a device for driving the double seat valve. This drive device has the function to realise the opening and closing movement of the above-mentioned double seat valve with the three closing parts by one single pressurised drive piston which is displaceable against the force of different springs. The double seat valve is not capable of seat cleaning, and thus, the known drive device does not have any driving means and displacement functions related to this in order to generate the partial stroke movement of the first and second closing part which is necessary for the respective seat cleaning.
It is the objective of the present invention to provide a device as simple as possible for driving a double seat valve which is capable of seat cleaning, opens toward the downside and switches without leakage, and which furthermore avoids a pressure-increasing direct impact on the closed seat region in the respective seat cleaning and ensures a discharge of the seat cleaning flow into and out of the leakage cavity that is as free of turbulences as possible.